The present invention relates to a method of fabricating non-volatile memory devices and, more particularly, to a method of fabricating a non-volatile memory device, which can prevent the formation of micro bridges between floating gates at the time of gate patterning.
In order to form the gate of a non-volatile memory device, a tunnel insulating layer and a first polysilicon layer for a floating gate are laminated over a semiconductor substrate. A trench is formed in an isolation region while patterning the first polysilicon layer and the tunnel insulating layer through an isolation process of self-aligned shallow trench isolation (SA-STI). The trench is gap-filled with an insulating material to form an isolation layer. A dielectric layer of an oxide-nitride-oxide (ONO) stack structure, a second polysilicon layer for a control gate, and a hard mask are sequentially laminated over the patterned first polysilicon layer and the isolation layer. The hard mask is etched using a photoresist pattern to cross the isolation layer. The second polysilicon layer, the ONO dielectric layer, and the patterned first polysilicon layer are patterned using the etched hard mask, thus forming a gate comprised of the tunnel insulating layer, the floating gate, the dielectric layer, and the control gate.
However, in the gate formation process, the first polysilicon layer is not fully removed. Minute poly residue remains causing the formation of a micro bridge between the floating gates. In particular, micro bridges are generated near the ONO dielectric layer, which remains after the last gate etching. This phenomenon becomes increasingly problematic when the height of the remaining dielectric layer is high.
In order to solve the above problem, a target etching thickness of the ONO dielectric layer can be increased. If a target etching thickness of the dielectric layer is increased, however, an attack margin of an active region decreases. The micro bridges result in a 2-bit failure, which makes it impossible to discriminate information between neighboring cells, thereby degrading product yield.